The present invention relates generally to x-ray tubes and, more particularly, to a convectively cooled x-ray target.
X-ray systems typically include an x-ray tube, a detector, and a bearing assembly to support the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then emits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in a computed tomography (CT) package scanner or an inspection CT device.
X-ray tubes typically include a cathode that provides a focused electron beam that is accelerated across an anode-to-cathode vacuum gap and produces x-rays upon impact with a disc-shaped anode target. Because of the high temperatures generated when the electron beam strikes the target, it is necessary to rotate the target at high rotational speed. The target is typically rotated by an iron stator structure with copper windings coupled to an induction motor having a cylindrical rotor built into a cantilevered axle that supports the target.
Traditionally, rotating anodes have a heat storage unit thermally attached to the rotating target that stores accumulated thermal energy during operation of the x-ray tube and dissipates the stored thermal energy via radiation heat transfer. Because the target is cooled primarily via radiation heat transfer, the cooling process is slow, and the peak power that can be applied to the focal spot is, thus, limited. Furthermore, the bulk temperature of the rotating target is a result of the average power that is applied, and, for increased average power applied to the target, the peak power that can be applied is further limited.
The operating conditions of newer generation x-ray tubes have placed increasing demands on x-ray tube targets. Image quality of for instance a CT system derives from the peak power that may be impinged on a target from the cathode. Image quality is also related to the size of the focal spot, and in recent years, the imaging industry has desired to decrease the size of the focal spot accordingly, thereby increasing the focal spot loading and the focal track loading. Furthermore, with increased gantry rotational speeds and more aggressive protocols, patient throughput has increased as well, thereby increasing the average power that is applied to an x-ray tube target and increasing stresses on the rotating anodes.
Therefore, it would be desirable to have an apparatus with efficient cooling of a target track therein to enable increased peak and average power which may be applied to the target track.